This invention relates to a process for producing unsaturated ketones especially unsaturated terpenoid ketones from correspondingly substituted propargyl alcohols.
The rearrangement reaction of a propargyl alcohol to an unsaturated ketone, which is a structural isomer thereof, under the influence of heat is generally known as "Oxy-Cope rearrangement". However, the particular, substituted propargyl alcohols which are used in the present invention have not been subjected to an Oxy-Cope rearrangement, nor is it known that a ketone having a terpenoid structure can be produced by this reaction. Briefly, the prior art relevant to a Oxy-Cope rearrangement reaction will be reviewed. "Oxy-Cope rearrangement" is a term which was coined by J. A. Berson et al who studied this reaction with cyclic compounds (J. Am. Chem. Soc. 86, 5017 and 5019 (1964)). Later, A. Viola et al studied the reaction of acyclic compounds in gaseous phase (J. Am. Chem. Soc. 87, 1150 (1965)). Thereafter, a number of workers did theoretical and applied researches on this reaction. However, as far as propargyl alcohols and its uses are concerned, only A. Viola et al (J.Am.Chem.Soc. 92, 2404 (1970)) are known to have used this reaction. They obtained the unsaturated ketone ##STR3## by heating 5-hexen-1-yn-3-ol ##STR4## in a gaseous phase at 350.degree. to 390.degree. C.
Typical conventional processes for the production of terpenoid compounds involve a multiple-step procedure comprising the Carroll rearrangement method using diketene which serves as a C.sub.3 element for chain extending or the Claisen rearrangement method using isopropenyl ether. For example, the steps which are needed for the production of pseudoionone starting with methyl heptenone may be illustrated as follows [See, e.g., U.S. Pat. No. 2,861,109, British Pat. No. 948,752, W. Kimel et al, J. Org. Chem. 23, 153 (1958) and R. Marbet et al, Angew, Chem., 72, 869 (1960)] ##STR5##
The chain extenders, diketene and isopropenyl ether, are comparatively expensive and such a step of including a chain extending reaction cannot be avoided.